Have tried several brands, weights and diameters of slugs in my .22 Dreamline with Slug A 600mm barrel and NSA 17.5 and 20.2 seem best so far but 100 yard groups are running around 2.5 to 3." 17.5s are going about 1000fps and 20.2s are going about 920fps. Any pointers or tuning tips to tighten...